1. Field of the Invention
The invention is concerned with the non-metallic fiber reinforcement of formable matrices used as structural material, such as concrete, plaster and sand-lime mixtures, and also to organic thermosetting type plastics and resins. The invention is particularly concerned with controlling the deterioration of such structural materials by alternate freezing and thawing, as well as improvement in flexural strength, namely in tension.
2. Description of the Prior Art
A relative weakness of certain hydraulic setting matrices used as structural materials, and also of organic thermosetting type plastics and resins, is well known. For example, concrete is strong in compression, but relatively weak in tension, and therefore in flexure. It is common for this reason to use steel reinforcement in concrete, and pre-stressing or post-stressing of the steel places the concrete in compression to counteract the flexural or tension loading.
Freeze-thaw cycles cause disruption of concrete for the same reason. Freezing of minute particles of ice inside the concrete cause tensile forces which are in excess of the ability to withstand them, causing portions (near the surface particularly) to spall.
It is known to admix fibers with the matrix to counteract these drawbacks. Among disclosures of steel or wire admixed fibers are the following:
______________________________________ Romualdi Patent No. 3,429,094 Ball et al Patent No. 3,650,785 National Standard Co., Technical Data Bulletin No. SWT-114, September, 1970. ______________________________________
The use of wire or steel fibers is unsatisfactory for several reasons. Steel has low elongation even at high tensile stresses and the fibers are likely to slip within the matrix when the structural member is subjected to loads. In addition to the relative stiffness and lack of workability of steel, it is relatively heavy and therefore costly to achieve a given proportionate volume within the matrix.
The use of non-metallic fibers admixed in matrices for strengthening purposes is equally well known. Examples of patents disclosing such compositions are the following:
______________________________________ Jarboe Patent No. 3,044,547 Shannon Patent No. 3,147,127 Fischer et al Patent No. 3,533,203 Zonsveld Patent No. 3,591,395 Goldfein Patent No. 3,645,961 Howe Patent No. 3,679,445 Kempster Patent No. 3,716,386 Kurtz Patent No. 3,769,052 ______________________________________
A characteristic of these fibers which creates a drawback is that under stress they begin to stretch, and in stretching their diameter shrinks. By shrinking, the fibers may lose their bond with respect to the matrix. This sequence causes rapid progressive failure when the yield strength of the composite fiber-matrix mixture is reached.
The same would be true of conventional reinforcing rod, except that it is preformed before use to provide mechanical connections with the matrix that persist regardless of shrinkage in cross section. This is not possible with extruded fibers which are merely cut off clean. A deformed fiber, such as some of the available metal ones or others see National-Standard Co. Specification No. SWT-114 and Howe U.S. Pat. No. 3,679,445) which have intermittent flattened or twisted sections, or crimped, hammered or tapered profiles, does not counteract this drawback. Other patents in this same general area discovered while conducting searches on the subject matter of this invention are the following:
______________________________________ Fischer et al Patent No. 3,208,838 Kjell-Berger Patent No. 3,217,075 Hull et al Patent No. 3,466,822 Gothard et al Patent No. 3,637,457 Campbell Patent No. 3,676,968 ______________________________________